Methods of providing water tightness to connectors by placing a watertight plug over the insulating sleeve of the wire are known in the art. Such watertight plugs usually have several circular ribs arranged around the main body of the plug which fit tightly against the inside wall of the connector cavity through which a connector contact is passed, thus providing water tightness of the connector.
Watertight plugs of this type are described in Japanese UM Publication No.-2976, Japanese UM Publication No. 85-71082 and Japanese UM Publication NO.87-134967. A typical example of such plugs is shown in FIG. 10. In the drawing, 200 is a watertight plug and 100 is a housing. In this conventional example of the watertight plug 200 there are three circular ribs 202. The water tightness is formed by resilient contact of tips 204 of these ribs 202 with the inside wall 104 of the cavity 102. However, since the watertight plugs are usually made of rubber or other elastic materials, pulling the wire 90 in the direction indicated by arrow A, as shown in the drawing, leads to the deformation of the rib 202 on the side of the direction in which the wire is pulled and to the formation of a gap G between the rib 202 and the inner wall 104 resulting in the failure of the watertight connection. Even if no gap G is formed, the tightness of the connection is reduced which can result in the loss of the water tightness. In other words, the amount of pressure that the seal can resist will be reduced, even if no gap results from bending the wire alone.
One of the proposed methods of solving this problem described in the Japanese UM Publication No. 86-194272 is directed to supplying a wire holder preventing the deformation of the wire 90 in the vicinity of the watertight plug when it is pulled. Japanese UM Publication No. 86-26272 describes a connector equipped with a means of the support of both watertight plug and the wire. However, these connectors have a complicated design and a large number of parts which makes them expensive, while the process of their production or assembly is labor intensive and difficult.
Ribs 202 of such conventional watertight plugs are made flexible to reduce the force required for the insertion of the plug in the cavity 102. On the other hand, the flexibility of the ribs is the reason of the problem described above. If the rigidity of the ribs 202 is increased, the resistance to the insertion is also increased, making the insertion difficult, especially in connectors having many contacts.